1. Field of the Invention
The present invention relates to an embedding resin (filling resin) for embedding an electronic part such as chip capacitor, chip inductor and chip resistor in a wiring circuit board (wiring board or wiring substrate), a wiring circuit board having an electronic part embedded therein and a process for producing a wiring circuit board using the embedding resin. More particularly, the present invention is suitable for multi-layer wiring circuit board, package for receiving semiconductor element, etc.
2. Description of the Related Art
In recent years, a multi-chip module (MCM) having a number of semiconductor elements mounted on a build-up wiring circuit board has been studied. An electronic part such as chip capacitor, chip inductor and chip resistor is, normally surface-mounted on amounting wiring layer formed on the surface of a wiring circuit board with a solder.
However, when electronic parts are surface-mounted on the surface of a build-up wiring circuit board, a predetermined mounting area corresponding to individual electronic parts, naturally restricting the miniaturization of the wiring circuit board. In some arrangement (treatment) of wiring during the surface mounting, parasitic impedance which is undesirable from the standpoint of properties increases, causing a problem that the use of electronic equipment at higher frequencies can be difficultly coped with.
In order to solve these problems, various methods involving the embedding of electronic parts in the wiring circuit board have been studied. Japanese Patent Laid-Open No. 1999-126978 discloses a method which comprises previously solder-mounting an electronic part on a wiring circuit board with a transferring sheet made of a metallic foil, and then transferring the electronic part to another wiring circuit board. However, this method leaves something to be desired in accuracy of positioning during mounting, etc. Japanese Patent Laid-Open No. 2000-124352 discloses a multi-layer wiring circuit board having an insulating layer built-up on an electronic part embedded in a core substrate.
The method involving the embedding of an electronic part in a core substrate requires that the gap between the core substrate and the electronic part be filled with a resin and the electrode of the electronic part and the wiring formed on the insulating layer be connected to each other by electroless plating or the like. In this case, an ordinary embedding resin cannot be provided with a sufficient adhesion to a deposit (plating) as a wiring, causing a problem of deposit blister (e.g., 29 of FIG. 5) in a reliability test. A wiring circuit board having a capacitor incorporated therein is disadvantageous in that the reliability in adhesion of wiring decreases when a large current flows as in a power supply wiring formed on an embedding resin having a capacitor embedded therein. However, no embedding resin aimed at improvement of adhesion of deposit has been studied.
An object of the invention is to provide an embedding resin which can enhance the mounting density of wiring circuit board having electronic parts mounted thereon and exhibit a high reliability in a reliability test such as impact resistance test and water resistance test, a wiring circuit board using the embedding resin and a process for producing a wiring circuit board using the embedding resin.
The embedding resin of the invention comprises at least one of a soluble resin and a soluble organic filler incorporated therein as a soluble component which can be dissolved with an oxidizing agent. By selectively dissolving and removing the soluble resin and soluble organic filler contained in the embedding resin with an oxidizing agent, the surface of the embedding resin can be easily roughened to exert an anchoring, effect required to obtain a desired adhesion of wiring. As a result, even a wiring circuit board having a capacitor incorporated therein can be provided with minimized drop of reliability in adhesion of wiring also when a large current flows as in a power supply wiring formed on an embedding resin having a capacitor embedded therein.